The etching of silicon and silicon compounds such as silicon dioxide and nitride in a gas plasma has been disclosed in connection with the manufacture of integrated circuits. Plasmas formed from fluorocarbons and fluorocarbon mixtures with oxygen are described, for example in U.S. Pat. Nos. 3,615,956 and 3,795,557. One disadvantage of such processes is that silicon is etched more rapidly than silicon dioxide. Therefore, in etching a layer of silicon dioxide on silicon, it is difficult to stop the process before an unacceptable amount of etching of the silicon surface takes place. Accordingly, the process becomes impractical and either a wet etch process must be used when etching the oxide or the plasma etch must be stopped short of the silicon surface and the etching of the oxide layer completed by wet etching.
Mixtures of hydrogen and fluorocarbons have been used to obtain a favorable etch rate ratio of silicon dioxide to silicon but the reaction is difficult to control and can result in polymer formation which stops the etching. A process has now been found which permits the etching of silicon dioxide layers to silicon using certain CF.sub.4 and oxygen gas mixtures.